Thallus: foliose, multi-lobed, attached by few to several holdfasts with 5-12 mm wide lobes upper surface: gray with epinecral layer consisting of air-filled hyphae upper cortex: 60-120 µm thick, hyaline with the outermost part (ca 10 µm) brownish medulla: 70-220 µm thick, turning reddish or reddish brown with Melzer's iodine lower cortex: 40-70 µm thick with the outermost part (c. 10 µm) light brown to brown lower surface: light brown, usually reticulate at least partly Perithecia: obpyriform to globose, 210-320 µm high and 180-300 µm wide, with hyaline exciple which is brown in the uppermost part asci: clavate or cylindrical, 8-spored ascospores: simple, hyaline, (8.5)10-13.5(-16) x (4.5-)5.5-7(-8.5) µm Pycnidia: not found in Sonoran material, elsewhere rare, immersed, ostiolum similar to that of the perithecium conidia: bacilliform, 5-6 x 1 µm Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: rocks at higher elevations World distribution: bipolar, arctic or at higher altitudes Sonoran distribution: only known from the San Francisco Peaks, Arizona at 3550 m. Notes: Dermatocarpon polyphyllizum is an arctic species with its main distribution at high elevations. It shows polymorphism concerning the lobe-number, there are present both multilobed and single-lobed specimens. The Sonoran specimen was, however, multilobed.